Hello Fitz, thank you for your response - It is very helpful to hear of your experiences and the lessons you've learnt.
You've absolutely right that there are many forms of damp and that there are different approaches to each of them. We seem to have just about all of them around the property.
One thing I've only recently realised is just how far water can track - We had a leak in the roof of the house which tracked across half of the building and appeared on a wall quite some distance away - It must have been tracking a good 5 meters at roof level before it went down the wall.
As mentioned the order in which we are tackling the work has completely changed with the extension, but our general remedial plan before we even start doing any interior work on each building is:
- Make sure the guttering and roofing is sound, including the pointing around the edge of the tiles (Some of our roofs are slate and the pointing around the perimeter is an issue)
- Make sure the walls themselves are in good condition (The house and outbuilding both have really poor pointing, in some places I think water can track straight through)
- Sort out the surrounding ground level, remove close trees and add french drains around the main house.
That will probably do most of the work as you mention, certainly a lot of the damp issues for the main house and the outbuilding are related to ground level and poor wall / roof condition.
You're right I haven't properly tested the damp level and will certainly be using the oven trick so thank you for that, but in some places you can tell from the clusters of woodlice, damp looking plasterboard or peeling plaster / paint.
I'm still unsure about the chemical DPC. I think that a lot of the issues people have are down the the number of different causes of damp, although even issues such as the surrounding ground level should in theory be resolved by a chemical DPC as long as it's not too high. I have seen others mention that they have had excellent results with dryrods though so I don't doubt that they will work if the problem is indeed rising damp. I suppose in our case, it's the question of whether or not we should bother after resolving everything else and if we want to risk doing all of the other work only to have to come back and add a DPC later. I'm leaning towards doing it on the workshop and outbuilding anyway as they are smaller buildings and it's easy to do while they are not full. It's easier to add french drains around the house so we might rely on those instead for the house.
My biggest concern is what then comes after - Not creating a new problem when adding insulation.
The new extension handles that by using a full cavity wall and for the roof we've specced a warm roof even on the pitched section - Bypassing the problem of roof ventilation altogether. For the other roofs, ventilation will need to be added as currently they are quite open but that needs to be retained as insulation is added.
For the various outbuildings, I'm still torn on the walls. For the garage we need to go down the cavity as the building regs call for it to be done properly, so after that work we should have a proper feel for how involved it is to add the required ventilation and cavity trays. I think having the experience from that project will then help with the outbuilding and workshop - But the nagging question for me is whether or not it's necessary to go to that effort for a building with low occupancy, as you've mentioned. If the work is easier than it initially seems then we might as well go down that route so being forced to learn how to do it for the garage isn't a bad thing.
Either way it's not simple - The are many different factors at play so the best we can do is learn what we can with the first projects and then apply that going forward.
It's annoying that there are so many cowboys in the industry - It forces us all to go down the rabbit hole but then again learning new skills is never a bad thing.
